Correct me if I am wrong. You want to access your machine running Ubuntu remotely from your mac and when you 'ssh' into your Ubuntu and when you try to 'echo $DISPLAY' you get an empty response. Probably the following solution might not work in your case, but give it a try if what you were trying is similar to what I have tried.
As you have already found one has to find the DISPLAY variable first.
So in your mac if you type as a normal user
echo $DISPLAY
Then what you would get is something like the following (It is the case in your hand). Anyway you all would see something similar in your systems.
/private/tmp/com.apple.launchd.0aQYNoXMFK/org.xquartz:0
Then try something like
xeyes
And now you know that your display is working
Now if you want to try the same as root (Please don't jump on me guys, I know some of you all are strongly against root access), but if does not work then in your root prompt do the following
export DISPLAY=/private/tmp/com.apple.launchd.0aQYNoXMFK/org.xquartz:0
The same you found in your normal user account. Then copy your '.Xauthority' at '/Users/normal user/.Xauthority' to '/var/root/'. The .Xauthority file is already there, but this would over right it.
cp /Users/normal user/.Xauthority /var/root/
Of course the export might work, but there is no harm in doing the above. Now try the following.
echo $DISPLAY
And you should see the following
/private/tmp/com.apple.launchd.0aQYNoXMFK/org.xquartz:0
If you 'ssh' into Ubuntu from normal user prompt then you do not need to do the root part, but since, I use root to 'ssh' my Ubuntu systems I often have to do this.
Then when you 'ssh into Ubuntu type
echo $DISPLAY
And you would see something like the following
localhost:10.0
The above would work if you have done all those other bits like forwarding and etc.
Again, if you want to use root in your Ubuntu and if the 'echo $DISPLAY' does not produce any response, then try the following (Assuming you are at root prompt).
cp /home/user name/.Xauthority /root/.Xauthority
Now try
echo $DISPLAY
again and you would see something like the following
localhost:10.0
For fun try
xeyes
And it works in my case. Hope this is helpful and would solve a problem like the one above or like mine that someone has come across and who spent a few hours on this problem while scratching head and trying to pull hair out like me :-)).
ssh -X -vvv root@xxxx
to see what is going on there./usr/bin/xauth: file /root/.Xauthority does not exist
, weird. It actually exists with permission 0600